Many supermarkets now have an entire aisle or half an isle dedicated to water. Dozens of different brands of plain old water, plus many processed in special ways that they claim makes them “healthier”.

One of the newest health kicks is drinking “alkaline” water, which supposedly has numerous health benefits. Meanwhile my dentist tells me that the carbonated water I drink (made with my own tap water) is too acidic for my teeth.

A quick explainer: Purified water is neither acidic nor basic (alkaline). It has a pH of 7, essentially neutral.

I am not a drinking water specialist, and I rarely buy bottled water. But I do know that for crops, not all water is the same. And most food crops hate alkaline water, preferring it slightly acidic.

Groundwater from wells generally contains certain salts related to the soil strata where it originates. These salts make the water more alkaline. How much more alkaline depends on which salts, and how much of them. Too much — or too many — makes the water toxic to most plants.

Over time, the salts from groundwater build up in the top layer of soil and changing its pH. This can begin to effect plant health, especially in areas where little rain falls — or during a drought. It can become obvious even over a single growing season if there is a long enough period without rain, such as this year.

Purifying water for agriculture on a large scale is prohibitively expensive. And for farming, the best water is free. Rain is generally pH neutral or even slightly acidic. If enough of it falls, it washes the salts out of the top layer of soil and decreases the pH.

The effect that a good rainstorm has on irrigated plants is almost immediate. In the case of the recent September storm, many of our crops experienced a massive growth spurt within a few days of the rain — easily visible from a hundred feet away.  The kale in your boxes today, for example, doubled in size in seven days.

The rain’s effects were less obvious on our fields that are irrigated with water from Lake Berryessa. That water is less alkaline than our groundwater — although still not technically “acidic”.

But there’s another big advantage to rainfall.  Any time we are irrigating at Terra Firma, we are using pumps that are at least partially fossil-fuel powered. We shut our pumps off a couple of days before the storm arrived, and are just now turning them back on again — unheard of for us in September here. Rainwater is not just free low-alkaline, it’s is also carbon-neutral.

That’s a “triple win”.